Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Ring-closing metathesis wikipedia , lookup
Kinetic resolution wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Hofmann–Löffler reaction wikipedia , lookup
Wolff–Kishner reduction wikipedia , lookup
Tiffeneau–Demjanov rearrangement wikipedia , lookup
Petasis reaction wikipedia , lookup
Hydroformylation wikipedia , lookup
CAPE CHEMISTRY UNIT II MODULE I Alcohols and phenol and Alkenes Worksheet and Revision guide 1. First part of homework - Due October 3, 2008 (a) Describe the reaction of butan-2-ol with iodine in sodium hydroxide. (b) Describe the reaction between phenol and sodium hydroxide 2. Classwork (websites for additional notes included with each section) (a) The structure of alcohols Alkyl group- + -OH Oxygen more electronegative than carbon and hydrogen C is +, H is + and O is Note – bent structure around O which have 2 lone pairs (b) Classes of alcohol http://www.chemguide.co.uk/organicprops/alcohols/background.html#top The carbon bearing the –OH group: Primary - has one R group and two hydrogens Secondary - has two R groups and one hydrogens Tertiary - has three R groups (c) Two types reaction of alcohols Fission of the RO-H bond Fission of the R-OH bond Alcohols has tendency for H+ to dissociate in presence of a base Alcohols act like acids [weaker acid than water] (d) Fission of RO-H bond http://www.chemguide.co.uk/organicprops/alcohols/sodium.html#top (i) reaction with sodium H2(g) and Na alkoxide ethanol + Na H2(g) + Na ethoxide propanol + Na H2(g) + Na propoxide (ii) reaction with carboxylic acid (esterifcation) http://www.chemguide.co.uk/organicprops/alcohols/esterification.html#top propanol and butanoic acid propyl butanoate + water butanol and propanoic acid butyl propanoate + water Catalyst – HCl or conc. H2SO4 (e) Fission of the R-OH bond (i) Halogenation using: HCl, HBr, HI, PBr3, PCl5 [mention only] CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 1 OF 9 (ii) Dehydration – reaction with conc. H2SO4 (as catalyst) http://www.chemguide.co.uk/organicprops/alcohols/dehydration.html#top A primary alcohol reacts with cold concentrated sulphuric acid to form alkyl hydrogensulphate : Ethanol + conc. sulphuric acid Ethyl hydrogensulphate + Water If the alcohol is in excess and the reaction mixture is warmed to 140oC, an ether is formed Ethyl hydrogensulphate + ethanol (excess) Diethyl ether (ethoxyethane) +sulphuric acid If the concentrated sulphuric is in excess and the temperature is raised to 170oC, water is eliminated, with the formation of an alkene: ethyl hydrogensulphate + conc. sulphuric acid (excess) ethene + sulphuric acid Dehydration – mainly 3o alcohol – carbocation stabilized by alkyl groups (iii) oxidation Combustion of 1o, 2o and 3o– degradation of C skeleton CO2, H2O Reaction with oxidants - maintain C skeleton Reactions with: KMnO4 / H+; K2Cr2O7 / H+ Or Na2Cr2O7/ H+ http://www.chemguide.co.uk/organicprops/alcohols/oxidation.html#top KMnO4/H+ is a stronger oxidizing agent than K2Cr2O7 Oxidation product depends on the class of alcohol With K2Cr2O7 / H+ or Na2Cr2O7 / H+ 1 – oxidized to aldehydes and further oxidation to carboxylic acid if temperature is raised or if aldehyde is not distilled off 2o - oxidized to ketones 3o – resistant to oxidation o With KMnO4/H+ 1 – oxidized directly to carboxylic acid 2o - oxidized to ketones o Primary alcohol Primary alcohol: -OH on C with 2 hydrogens attached [-OH on C attached to 1 other C] During oxidation: [-2H] one from –OH and one other Result – aldehyde Aldehyde: 1 H attached to the carbonyl C Further oxidation to the carboxylic acid CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 2 OF 9 To obtain the aldehyde – distill off as it is formed Aldehyde has lower b.p. than alcohol – no hydrogen bonds. Primary alcohol aldehyde carboxylic acid e.g. propan-1-ol, propanaldehyde, propanoic acid Secondary alcohol With KMnO4/H+, K2Cr2O7 / H+ or Na2Cr2O7 / H+ Secondary alcohol: -OH on C with 1 hydrogen attached [-OH on C attached to 2 other C] During oxidation: [-2H] one from –OH and one other Result – ketone The carbonyl carbon in a ketone does not have a hydrogen- no further oxidation (ketones resist oxidation) Tertiary alcohol Tertiary alcohol: -OH on C with 0 hydrogen attached [-OH on C attached to 3 other C] No oxidation except under extreme conditions Iodoform reaction - (to be done again in aldehydes and ketones) http://www.chemguide.co.uk/organicprops/alcohols/iodoform.html#top Alcohols with the formula CH3CH(OH)R [ethanol if R = H] are oxidized by sodium iodate (I) to CH3COR and therefore give a positive iodoform test. In the formula CH3CH(OH)R: The alpha carbon is CH3. The alpha carbon is one carbon away from the carbon with the functional group. Iodoform is CHI3: Tri-iodomethane (fine yellow crystals with characteristic smell) Stage 1: alcohol is oxidized to a carbonyl compound Example: Ethanol in the presence of I2 / NaOH Ethanal Stage 2: The 3 hydrogens on the alpha carbon are replaced with iodine Example: ethanal in the presence of I2 / NaOH Tri-iodo-ethanal Stage 3: The excess base hydrolyses the molecule and causes the C-C bond to break, releasing triiodomethane [CHI3]. Example: Tri-iodo-ethanal in the presence of OH- Tri-iodomethane + the methoxide anion CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 3 OF 9 From Chemguide: Summary of the reactions during the triiodomethane (iodoform) reaction We will take the reagents as being iodine and sodium hydroxide solution. (e) (f) The structure of phenol http://www.chemguide.co.uk/organicprops/phenol/background.html#top Phenol will be look at again after the topic BENZENE From Chemguide: The structure of phenol The simplest way to draw the structure of phenol is: CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 4 OF 9 There is an interaction between the delocalised electrons in the benzene ring and one of the lone pairs on the oxygen atom. This has an important effect on both the properties of the ring and of the -OH group. One of the lone pairs on the oxygen overlaps with the delocalised ring electron system . . . . . . giving a structure rather like this: The donation of the oxygen's lone pair into the ring system increases the electron density around the ring. That makes the ring much more reactive than it is in benzene itself. It also helps to make the -OH group's hydrogen a lot more acidic than it is in alcohols. The -OH group attached to the benzene ring in phenol has the effect of making the ring much more reactive than it would otherwise be. For example, as you will find below, phenol will react with a solution of bromine in water (bromine water) in the cold and in the absence of any catalyst. It also reacts with dilute nitric acid, whereas benzene itself needs a nitrating mixture of concentrated nitric acid and concentrated sulphuric acid. Reaction with bromine water http://www.chemguide.co.uk/organicprops/phenol/ring.html#top If bromine water is added to a solution of phenol in water, the bromine water is decolourised and a white precipitate is formed which smells of antiseptic. CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 5 OF 9 The precipitate is 2,4,6-tribromophenol. Notice the multiple substitution around the ring - into all the activated positions. (The 6- position is, of course, just the same as the 2- position. Both are next door to the -OH group.) Note: Bromine water is normally used as a test for a C=C double bond. The important difference with phenol is the formation of a white precipitate as well as the bromine water being decolourised. If you choose to follow this link, use the BACK button on your browser to return to this page. Combustion of phenol http://www.chemguide.co.uk/organicprops/phenol/other.html#top Phenol burns in a plentiful supply of oxygen to give carbon dioxide and water. However, for compounds containing benzene rings, combustion is hardly ever complete, especially if they are burnt in air. The high proportion of carbon in phenol means that you need a very high proportion of oxygen to phenol to get complete combustion. Look at the equation. As a general rule, the hydrogen in a molecule tends to get what oxygen is available first, leaving the carbon to form carbon itself, or carbon monoxide, if there isn't enough oxygen to go round. Phenol tends to burn in air with an extremely smoky flame - full of carbon particles. Esterification of phenol http://www.chemguide.co.uk/organicprops/phenol/other.html#top You will probably remember that you can make esters from alcohols by reacting them with carboxylic acids. You might expect phenol to be similar. However, unlike alcohols, phenol reacts so slowly with carboxylic acids that you normally react it with acyl chlorides (acid chlorides) or acid anhydrides instead. CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 6 OF 9 Making esters from phenol using an acyl chloride A typical acyl chloride is ethanoyl chloride, CH3COCl. Phenol reacts with ethanoyl chloride at room temperature, although the reaction isn't as fast as the one between ethanoyl chloride and an alcohol. Phenyl ethanoate is formed together with hydrogen chloride gas. Sometimes it is necessary to modify the phenol first to make the reaction faster. For example, benzoyl chloride has the formula C6H5COCl. The -COCl group is attached directly to a benzene ring. It is much less reactive than simple acyl chlorides like ethanoyl chloride. In order to get a reasonably quick reaction with benzoyl chloride, the phenol is first converted into sodium phenoxide by dissolving it in sodium hydroxide solution. The phenoxide ion reacts more rapidly with benzoyl chloride than the original phenol does, but even so you have to shake it with benzoyl chloride for about 15 minutes. Solid phenyl benzoate is formed. Making esters from phenol using an acid anhydride A typical acid anhydride is ethanoic anhydride, (CH3CO)2O. The reactions of acid anhydrides are slower than the corresponding reactions with acyl chlorides, and you usually need to warm the mixture. Again, you can react the phenol with sodium hydroxide solution first, producing the more reactive phenoxide ion. CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 7 OF 9 If you simply use phenol and ethanoic anhydride, phenyl ethanoate is formed together with ethanoic acid. This reaction isn't important itself, but a very similar reaction is involved in the manufacture of aspirin (covered in detail on another page - link below). If the phenol is first converted into sodium phenoxide by adding sodium hydroxide solution, the reaction is faster. Phenyl ethanoate is again formed, but this time the other product is sodium ethanoate rather than ethanoic acid. Properties of phenol as an acid http://www.chemguide.co.uk/organicprops/phenol/acidity.html#top With indicators The pH of a typical dilute solution of phenol in water is likely to be around 5 - 6 (depending on its concentration). That means that a very dilute solution isn't really acidic enough to turn litmus paper fully red. Litmus paper is blue at pH 8 and red at pH 5. Anything in between is going to show as some shade of "neutral". With sodium hydroxide solution Phenol reacts with sodium hydroxide solution to give a colourless solution containing sodium phenoxide. In this reaction, the hydrogen ion has been removed by the strongly basic hydroxide ion in the sodium hydroxide solution. CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 8 OF 9 With sodium carbonate or sodium hydrogencarbonate Phenol isn't acidic enough to react with either of these. Or, looked at another way, the carbonate and hydrogencarbonate ions aren't strong enough bases to take a hydrogen ion from the phenol. Unlike the majority of acids, phenol doesn't give carbon dioxide when you mix it with one of these. This lack of reaction is actually useful. You can recognise phenol because: It is fairly insoluble in water. It reacts with sodium hydroxide solution to give a colourless solution (and therefore must be acidic). It doesn't react with sodium carbonate or hydrogencarbonate solutions (and so must be only very weakly acidic). With metallic sodium Acids react with the more reactive metals to give hydrogen gas. Phenol is no exception - the only difference is the slow reaction because phenol is such a weak acid. Phenol is warmed in a dry tube until it is molten, and a small piece of sodium added. There is some fizzing as hydrogen gas is given off. The mixture left in the tube will contain sodium phenoxide. CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC – ALCOHOLS & PHENOL PAGE 9 OF 9